DESCRIPTION: The biological consequences of a single alpha particle traversal through either the nucleus or cytoplasm of a cell are unknown. With the availability of the microbeam facility at the Radiological Research Facility, we show recently that a single alpha traversal through the nucleus of AL cells (average nuclear cross sectional area 108 m m2) resulted in a mutagenic incidence 2 times that of background. In addition, multiplex PCR analysis of mutant DNA showed that the proportion of mutants with multilocus deletions increased with the number of alpha particle traversals. Preliminary data also suggest that irradiation of cellular cytoplasm alone with 4 or more alpha particles induces mutation at the S1 locus at a frequency two fold above the spontaneous level. The overall goals of this proposal are 1) To examine both the quantitative mutagenic yield and the spectrum of mutations induced by either a single or a defined number of alpha particle traversals targeted at cellular cytoplasm; and 2) To examine the cellular and biochemical mechanisms leading to these mutational events, particularly, the roles of reactive oxygen species and cellular glutathione levels. A series of 5 specific aims are proposed to address 3 testable hypotheses. Mutation will be scored at the S1 locus using the human-hamster hybrid AL cells. The AL cell line contains only one copy of human chromosome 11 and mutations on marker genes located on this chromosome can be readily scored using an antibody complement lysis technique. By using specific DNA probes of other genes that have been regionally mapped to various sites on chromosome 11, the molecular mechanisms of mutation in AL cells will also be examined.